For years, military personnel have used image intensifier night vision goggles (NVG) to conduct night operations. The majority of the fielded version of these NVGs comprise of objective lenses, image intensifier tubes and eyepieces usually assembled in a straight line. Thus, most prior art night vision goggles extend out in front of the user's face and normally block his/her forward view. An exception to this type of configuration is a fielded aviation goggle called Catseyes, in which the eyepiece has an offset and a see-through prism. This goggle, while not blocking the forward view of the user, still, however, extends out from the user's face. Another exception is a special use goggle for parachute operation called the Eagle Eye System, originally purchased by Canadian Armed Forces for Search and Rescue Technicians. This device uses folded see-through optics. While the folded optics presents a low profile NVG, the device sacrifices eye relief and range performance found in other fielded NVGs. The operation of each of these night vision goggles is similar. An objective lens collects light from a low illumination scene and focuses it onto a photocathode of an image intensifier tube. The image intensifier tube photocathode converts this image into an electronic signal which is amplified and reconverted into an intensified image on the image tube's screen. An eyepiece magnifies the image tube screen image for viewing by a user.
Since most NVGs used in the military extend out from the user's face, the military has been forced to modify their tactics at night. Individual soldiers can not perform their normal daylight movement techniques such as a low crawl, firing from a prone position or a quick forward rush and drop to the ground. This variation in tactics requires additional training. By design and limitation in technology, image intensifier tubes either shut off or operate with severely degraded resolution when the light level increases. Since the standard NVGs block the forward vision, users become blind when they are suddenly exposed to high light conditions. However, if an NVG were a "see-through" device, the user's normal eyesight would take over under high light conditions. For operations in urban areas, lack of a "see-through" capability represents a major shortcoming. Furthermore, lack of ballistic and laser protection (BLPs) forces soldiers to wear a BLPS behind the NVG, pushing it out so far that it reduces the intensified field of vision (FOV). The known prior art systems do not combine the performance characteristics and enhancements of the night vision visor system according to the present invention.
In further consideration of the optics associated with prior art devices, it is known that several devices use a single objective to image a scene on a single image intensifier, and split the output (ocular) side into two paths for each eye using mirrors or prisms. These devices include the U.S. Army's PVS-7 Binocular Night Vision Goggle, disclosed in U.S. Pat. No. 5,712,726, as well as the SIMRAD GN 1 Night Vision Compact Monocular Goggle for night time vision. Another prior art device is represented in U.S. Pat. No. 4,653,879 issued to Filipovich. In this patent, the night vision device images a scene onto two separate image intensifiers/ocular paths, using conventional optical lenses and beam combing prisms to fold the device into a compact structure. Another device is disclosed in U.S. Pat. Nos. 5,699,194 and 5,701,202, issued to Takahashi, which uses an aspheric beam combiner to directly superimpose an electronically generated scene onto a direct view scene. However, significant drawbacks associated with each of these systems exist, including the lack of one or more of the following features: low profile architecture (to user's head), direct view (see through) capability, low weight, peripheral direct view, interpupilliary adjustment, and a 40.degree. field of view. Neither the PVS-7 device, nor the SIMRAD GN 1 device are see-through night vision devices. Furthermore, the GN 1 device lacks an interpupilliary adjustment, while the system disclosed in the Filipovich patent includes a limited field of view and a relatively heavy structure. The devices disclosed in the Takahashi patents includes two further difficulties. The Takahashi system uses total internal reflection, which can be obscured by contaminants or poor polishing and can not use diamond turning. Moreover, since it has only three surfaces to correct aberrations, its performance in obtaining both resolution and field of view is relatively poor.
Still further, most prior art systems fail to provide robust packaging, thereby permitting device and container breakage. Other shortcomings of prior art systems include the failure of such systems to provide a compact low profile device, excessive weight of such devices causing head/neck strain and fatigue problems and the lack of laser protection or ballistic protection from projectile fragments. In addition, the prior art device can not be used as an integrated sun, wind and dust protective visor and fails to provide a full 40 degree field of view to the user. Prior art systems have also failed to incorporate a forward-looking photo transistor to turn the system off in sufficiently lighted areas, as well as a forward projecting infrared light emitting diode for additional illumination in completely dark areas, in addition to a user adjustable image intensifier variable gain capability. The above shortcomings of the prior art devices, which also include failure to optimize objective lens locations for addressing stereopsis and failure to provide means of secondary image input, would make a night vision device which incorporates such features highly desirable.
The night vision device according to the present invention provides many system enhancements over the previously designed systems. Such enhancements include a system housing constructed from lightweight composite materials helping to reduce head/neck fatigue; and a very compact and low profile structure optimizing the center of gravity, to further reduce head/neck fatigue. The device according to the present invention further includes a forward projecting infrared light emitting diode (IRLED) for additional illumination in completely dark areas; and an enclosed face mask type housing which provides sun, wind, and dust protection. A front visor attached to the mask housing provides various levels of environmental protection, including both laser and ballistic protection.
The system is designed to remain compatible with usage of the PASGT helmet and incorporates a user adjustable image intensifier variable gain capability, provides for secondary image input for direct view or electronic read out sensors, and provides full 40 degree field of view. The system of the present invention also optimizes objective lens location, thereby minimizing effects of stereopsis, and utilizes an image intensifier tube that is smaller in size with minimal reduction in active diameter relative to the prior art tube in use in the AN/PVS-7 system.
The small tube size allows smaller system package and folded optics to provide see-through capability. The smaller components and folded optics form a low profile system which minimizes the chance of the device being caught on branches, tree limbs and the like.
The night vision visor system according to the present invention achieves the features of low profile architecture, direct view, low weight, peripheral direct view, interpupilliary adjustment and 40.degree. field of view by utilizing a low density (specific gravity 1.1) plastic multi-aspheric beam combiner which has internal surface with optical power. The optical power reduces the size of the internal light beam so that the beam combiner can have a depth of less than 40 mm, as compared to 70 mm with conventional glass beam combiner. The beam combiner also allows the direct viewing of visible scenes simultaneously with viewing of the same scene in the infrared. Furthermore, a relay lens with tilted components images the light which passes through the beam combiner with the correct amount of distortion and other image aberrations to cancel the distortions and other aberration inherent in a plastic multi-aspheric beam combiner.